(a) What type of a cell is the lead storage battery ? Write the anode and the cathode reactions and the overall reaction occuring in a lead storage battery while operating .
(b) A voltaic cell is set up at `25^(@)C` with the half-cells , `Al|Al^(3+) (0.001M)` and `Ni| Ni^(2+) (0.50 M)`. Write the equation for the reaction that occurs when the cell generates an electric current and determine the cell potential.
(Given : `E_(Ni^(2+)|Ni)^(@) = -0.25 V , E_(Al^(3+)|Al)^(@) = -1.66V`).

Explanation

The lead storage battery is the most important secondary cell .
The cell reactions when the battery is in use are given below .
At Anode : `Pb(s) + SO_(4)^(2-) (aq) to PbSO_(4)(s) + 2e^(-)`
At Cathode : `Pb O_(2)(s) + SO_(4)^(2-) (aq) + 4H^(+)(aq) + 2e^(-) to PbSO_(4) (s) + 2H_(2)O(l)`
The overall equation is
`Pb(s) + PbO_(2) (s) + 2 H_(2)SO_(4)(aq) to 2PbSO_(4)(s) + 2H_(2)O(l)`
Half cell equations are :
`{:(Al to Al^(3+) + 3e^(-) ,, "(At Anode)"), (Ni^(2+) + 2e^(-) to Ni ,, "(At Cathod)"), (2Al + 3Ni^(2+) to 2 Al^(3+) + 3Ni ,,"(Over all reaction)"):}`